The present invention relates to a non-continuous sensing apparatus for a temperature control, and more particularly to an improved electronic control device having reduced size and energy consumption.
There is shown in FIG. 1 a circuit diagram of a conventional heater drive controller by way of example. A heater 1p is power-supplied from an A.C. power source 18p through a bidirectional thyristor 2p connected in series with the heater 1p. The thyristor 2p is gated by a control signal input to its gate terminal from a comparator 4p which is devised so as to generate the control signal according to an output of a resistance bridge 5p in which a temperature sensor 6p is contained as a bridge component. Both the comparator 4p and the bridge 5p are always supplied with a D.C. power from a D.C. voltage source 13p consisting of a rectifying diode 17p, a resistor 16p, a Zener diode 15p and a smoothing capacitor 14p. Comparing a sensor output with a reference voltage which corresponds to a predetermined control value of temperature, the comparator 4p outputs a switching-on trigger signal at the time of the zero-crossings of the A.C. power source 18 p. The trigger signal is fed to the thyristor gate 2p so as to energize the heater 1p while the bridge output continues to indicate that the temperature measured by the sensor 6p is lower than the predetermined control value of temperature.
In such a conventional device, the heat dissipation or the energy consumption in the control system is help being large, because the temperature sensor 6p and the comparator 4p are kept supplied with a current at all times during the operation of the device. In addition, in case the temperature sensor 6p, as is often the case, can not be chosen so as to have a large resistance value, the current to be supplied to the sensor must be increased to obtain a necessary sensitivity, and the problem of heat dissipation becomes more serious. Large dissipation of heat not only makes it difficult to assemble the whole device compactly but also causes the device to be damaged due to overheating.